Fungicidal imidazole dioxolane and 1,3-dioxane derivatives

ABSTRACT

The invention provides imidazole dioxolane derivatives of the general formula:    &lt;IMAGE&gt;  (I)  or an acid-addition salt or metal salt complex thereof, in which R represents an optionally substituted phenyl group; R1 represents a hydrogen atom or an optionally substituted alkyl or alkenyl group; R2 represents an optionally substituted alkyl group; and n is 1 or 2; processes for their preparation; compositions containing such compounds and their use as fungicides.

This invention relates to certain imidazole dioxolane and 1,3-dioxane derivatives, a process for their preparation, compositions containing such compounds and their use as fungicides.

According to the present invention there is provided a compound of the general formula ##STR2## or an acid-addition salt or metal salt complex thereof, in which R represents an optionally substituted phenyl group; R¹ represents a hydrogen atom or an optionally substituted alkyl or alkenyl group; R² represents an optionally substituted alkyl group; and n is 1 or 2.

When the compounds of this invention contain an alkyl or alkenyl substituent group, this may be linear or branched and may contain up to 12, preferably up to 6, carbon atoms.

When any of the foregoing substituents are designated as being optionally substituted, the substituent groups which are optionally present may be any one or more of those customarily employed in the development of pesticidal compounds, and/or the modification of such compounds to influence their structure/activity, persistence, penetration or other property. Specific examples of such substituents include, for example, halogen atoms, nitro, cyano, hydroxyl, alkyl, haloalkyl, alkoxy, haloalkoxy, amino, alkylamino, dialkylamino, formyl, alkoxycarbonyl, carboxyl, alkanoyl, alkylthio, alkylsulphinyl, alkylsulphonyl, carbamoyl and alkylamido groups. When any of the foregoing substituents represents or contains an alkyl substituent group, this may be linear or branched and may contain up to 12, preferably up to 6, and especially up to 4, carbon atoms.

It is preferred that R is a phenyl group substituted by 1 to 3 halogen, especially chlorine, atoms.

Preferably, R¹ represents a hydrogen atom, a C₁₋₁₂ alkyl, particularly a C₁₋₆ alkyl and especially a C₁₋₄ alkyl, group or a C₂₋₁₂ alkenyl, particularly a C₂₋₆ alkenyl and especially a C₂₋₄ alkenyl, group, each group being optionally substituted by one or more substituents selected from halogen atoms, nitro, cyano, hydroxyl, C₁₋₄ haloalkyl, C₁₋₄ alkoxy, C₁₋₄ haloalkoxy, amino, C₁₋₄ alkylamino, di-C₁₋₄ alkylamino, formyl, C₁₋₄ alkoxycarbonyl and carboxyl groups.

It is also preferred that R² represents a C₁₋₁₂ alkyl, particularly a C₁₋₆ alkyl, group.

A particularly preferred sub-group of compounds of formula I is that in which R represents a fluorophenyl, chlorophenyl, bromophenyl or dichlorophenyl group; R¹ represents a hydrogen atom or a methyl, ethyl, propyl, butyl or butenyl group; R² represents a methyl group; and n is 1 or 2.

It should also be appreciated that the compounds of formula I are capable of existing as different geometric and optical isomers. The invention thus includes both the individual isomers and mixtures of such isomers.

The present invention also provides a process for the preparation of a compound of formula I as defined above or an acid-addition salt or metal salt complex thereof which comprises reacting a compound of the general formula ##STR3## or an acid-addition salt or metal salt complex thereof, in which R and R² are as defined above, with a compound of the general formula ##STR4## in which R¹ and n are as defined above, in the presence of an acid and, if desired, reacting the compound of formula I so obtained with a suitable acid or metal salt to form an acid-addition salt or metal salt complex thereof.

It is preferred that the acid is a mild acid such as para-toluenesulphonic acid or methanesulphonic acid.

The process of the invention is conveniently carried out in the presence of a solvent. Suitable solvents include aromatic compounds, such as toluene. The reaction is suitably carried out at a temperature of 0° C. to 130° C., the preferred reaction temperature being 15° C. to 115° C.

Compounds of formula II and acid-addition salts or metal salt complexes thereof form the subject of our copending application (T 551). They can be prepared by reacting a compound of the general formula ##STR5## in which R is as defined above and R⁴, R⁵ and R⁶, which may be the same or different, represent an alkyl, cycloalkyl, phenyl or benzyl group, with a compound of the general formula ##STR6## in which R² is as defined above, in the presence of a base, and, if desired, reacting the compound of formula II so obtained with a suitable acid or metal salt to form an acid-addition salt or metal salt complex thereof. A particularly preferred compound of formula IV is that in which R⁴, R⁵ and R⁶ all represent an ethyl group.

Compounds of formula IV may be prepared according to the method described by D. Burkhouse and H. Zimmer in Synthesis, 1984, 330. Compounds of formula V may be prepared by the method described by R. G. Jones and K. C. McLaughlin in J. Amer. Chem. Soc., 1949, 71, 244.

Compounds of formula III are known compounds or can be prepared by processes analogous to known processes.

The compounds of general formula I have been found to have fungicidal activity. Accordingly, the invention further provides a fungicidal composition which comprises a carrier and, as active ingredient, a compound of formula I or an acid-addition salt or metal salt complex thereof as defined above. A method of making such a composition is also provided which comprises bringing a compound of formula I as defined above, or an acid-addition salt or metal salt complex thereof, into association with at least one carrier. Such a composition may contain a single compound or a mixture of several compounds of the present invention. It is also envisaged that different isomers or mixtures of isomers may have different levels or spectra of activity and thus compositions may comprise individual isomers or mixtures of isomers.

A composition according to the invention preferably contains from 0.5 to 95% by weight of active ingredient.

A carrier in a composition according to the invention is any material with which the active ingredient is formulated to facilitate application to the locus to be treated, which may for example be a plant, seed or soil, or to facilitate storage, transport or handling. A carrier may be a solid or a liquid, including a material which is normally gaseous but which has been compressed to form a liquid, and any of the carriers normally used in formulating fungicidal compositions may be used.

Suitable solid carriers include natural and synthetic clays and silicates, for example natural silicas such as diatomaceous earths; magnesium silicates, for example talcs; magnesium aluminium silicates, for example attapulgites and vermiculites; aluminium silicates, for example kaolinites, montmorillonites and micas; calcium carbonate; calcium sulphate; ammonium sulphate; synthetic hydrated silicon oxides and synthetic calcium or aluminium silicates; elements, for example carbon and sulphur; natural and synthetic resins, for example coumarone resins, polyvinyl chloride, and styrene polymers and copolymers; solid polychlorophenols; bitumen; waxes, for example beeswax, paraffin wax, and chlorinated mineral waxes; and solid fertilisers, for example superphosphates.

Suitable liquid carriers include water; alcohols, for example isopropanol and glycols; ketones, for example acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ethers; aromatic or araliphatic hydrocarbons, for example benzene, toluene and xylene; petroleum fractions, for example, kerosine and light mineral oils; chlorinated hydrocarbons, for example carbon tetrachloride, perchloroethylene and trichloroethane. Mixtures of different liquids are often suitable.

Fungicidal compositions are often formulated and transported in a concentrated form which is subsequently diluted by the user before application. The presence of small amounts of a carrier which is a surface-active agent facilitates this process of dilution. Thus preferably at least one carrier in a composition according to the invention is a surface-active agent. For example the composition may contain at least two carriers, at least one of which is a surface-active agent.

A surface-active agent may be an emulsifying agent, a dispersing agent or a wetting agent; it may be nonionic or ionic. Examples of suitable surface-active agents include the sodium or calcium salts of polyacrylic acids and lignin sulphonic acids; the condensation products of fatty acids or aliphatic amines or amides containing at least 12 carbon atoms in the molecule with ethylene oxide and/or propylene oxide; fatty acid esters of glycerol, sorbitol, sucrose or pentaerythritol; condensates of these with ethylene oxide and/or propylene oxide; condensation products of fatty alcohol or alkyl phenols, for example p-octylphenol or p-octylcresol, with ethylene oxide and/or propylene oxide; sulphates or sulphonates of these condensation products; alkali or alkaline earth metal salts, preferably sodium salts, or sulphuric or sulphonic acid esters containing at least 10 carbon atoms in the molecule, for example sodium lauryl sulphate, sodium secondary alkyl sulphates, sodium salts of sulphonated castor oil, and sodium alkylaryl sulphonates such as dodecylbenzene sulphonate; and polymers of ethylene oxide and copolymers of ethylene oxide and propylene oxide.

The compositions of the invention may for example be formulated as wettable powders, dusts, granules, solutions, of active ingredient and usually contain in addition to solid inert carrier, 3-10% w of a dispersing agent and, where necessary, 0-10% w of stabiliser(s) and/or other additives such as penetrants or stickers. Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant, and may be diluted in the field with further solid carrier to give a composition usually containing 1/2-10% w of active ingredient. Granules are usually prepared to have a size between 10 and 100 BS mesh (1.676-0.152 mm), and may be manufactured by agglomeration or impregnation techniques. Generally, granules will contain 1/2-75% w active ingredient and 0-10% w of additives such as stabilisers, surfactants, slow release modifiers and binding agents. The so-called "dry flowable powders" consist of relatively small granules having a relatively high concentration of active ingredient. Emulsifiable concentrates usually contain, in addition to a solvent and, when necessary, co-solvent, 1-50% w/v active ingredient, 2-20% w/v emulsifiers and 0-20% w/v of other additives such as stabilisers, penetrants and corrosion inhibitors. Suspension concentrates are usually compounded so as to obtain a stable, non-sedimenting flowable product and usually contain 10-75% w active ingredient, 0.5-15% w of dispersing agents, 0.1-10% w of suspending agents such as protective colloids and thixotropic agents, 0-10% of other additives such as defoamers, corrosion inhibitors, stabilisers, penetrants and stickers, and water or an organic liquid in which the active ingredient is substantially insoluble; certain organic solids or inorganic salts may be present dissolved in the formulation to assist in preventing sedimentation or as anti-freeze agents for water.

Aqueous dispersions and emulsions, for example compositions obtained by diluting a wettable powder or a concentrate according to the invention with water, also lie within the scope of the invention. The said emulsions may be of the water-in-oil or of the oil-in-water type, and may have a thick `mayonnaise` like consistency.

The composition of the invention may also contain other ingredients, for example other compounds possessing herbicidal, insecticidal or fungicidal properties.

Of particular interest in enhancing the duration of the protective activity of the compounds of this invention is the use of a carrier which will provide a slow release of the fungicidal compounds into the environment of the plant which is to be protected. Such slow-release formulations could, for example, be inserted in the soil adjacent to the roots of a vine plant, or could include an adhesive component enabling them to be applied directly to the stem of a vine plant.

The invention still further provides the use as a fungicide of a compound of the general formula I as defined above or an acid-addition salt or metal salt complex thereof or a composition as defined above, and a method for combating fungus at a locus, which comprises treating the locus, which may be for example plants subject to or subjected to fungal attack, seeds of such plants or the medium in which such plants are growing or are to be grown, with such a compound or composition.

The present invention is of wide applicability in the protection of crop plants against fungal attack. Typical crops which may be protected include vines, grain crops such as wheat and barley, rice and tomatoes. The duration of protection is normally dependent on the individual compound selected, and also a variety of external factors, such as climate, whose impact is normally mitigated by the use of a suitable formulation.

The invention is further illustrated by the following Examples.

EXAMPLE 1 (a) Preparation of 2,4-dichlorophenyl 1-methyl-5-imidazolylmethyl ketone

Butyl lithium (2.2 m, 21 ml) in hexane was added dropwise to a solution of diethyl 2,4-dichlorophenyl ethoxymethyl phosphonate (17.3 g, 45 mmol) in tetrahydrofuran (200 ml) at -78° C. under an atmosphere of nitrogen. The resulting deep red solution was stirred for 10 minutes and then treated with N-methyl 5-imidazolecarboxaldehyde (3.75 g, 34 mmol) dissolved in tetrahydrofuran (150 ml). After a further hour at -78° C., the reaction mixture was allowed to warm to room temperature whereupon it was treated with water and then acidified with concentrated hydrochloric acid (24 ml) and refluxed for 24 hours. After cooling, the tetrahydrofuran was evaporated and the aqueous residue was made basic with sodium carbonate and then extracted with ethyl acetate (2×300 ml). The combined organic extract was washed with saturated sodium chloride solution, dried and concentrated. The residue was then chromatographed on silica using 9:1 chloroform: methanol as eluant to give 2,4-dichlorophenyl 1-methyl-5-imidazolylmethyl ketone (8.01 g) as a white solid.

(b) Preparation of 2-(2,4-dichlorophenyl)-2-(1-methyl-5-imidazolylmethyl)-4-methyl-1,3-dioxolane (R=2,4-dichlorophenyl; R¹ =methyl; R² =methyl; n=1)

A mixture of the 2,4-dichlorophenyl 1-methyl-5-imidazolylmethyl ketone (0.9 g) obtained in (a), 1,2-propanediol (3 ml) and para-toluenesulphonic acid (0.85 g) in xylene (90 ml) was refluxed under a Dean-Stark apparatus for 20 hours and then cooled to room temperature. Chloroform (300 ml) was added and the resultant mixture was washed with aqueous sodium carbonate (2×100 ml) and then dried. Evaporation of the solvent left an oil which was chromatographed on silica gel using 19:1 chloroform: methanol as eluant to give the two enantiomeric pairs of 2-(2,4-dichlorophenyl)-2-(1-methyl-5-imidazolylmethyl)-4-methyl-1,3-dioxolane as oils. Sample A consisted of the (2R,4R) and (2S,4S) isomers and sample B consisted of the (2R,4S) and (2S,4R) isomers. Low resolution mass spectroscopy on a mixture of A and B revealed the mass/charge ratio of the parent molecule ion, M⁺, to be 327.

Analysis (for a mixture of A and B).

Calc. C: 55.2; H: 3.9; N: 8.6%.

Found C: 54.6; H: 3.9; N: 8.9%.

EXAMPLES 2 to 14

By processes similar to those described in Example 1 above, further compounds according to the invention were prepared as detailed in Table 1 below. In this table the compounds are identified by reference to formula 1. Low and high resolution mass spectroscopy and C,H,N analysis data for these compounds is given in Table IA.

                                      TABLE I                                      __________________________________________________________________________     Example                                                                        No.  Isomers         R         R.sup.1   R.sup.2                                                                            n                                 __________________________________________________________________________     2A   (2R,4R) & (2S,4S)                                                                              4-fluorophenyl                                                                           --CH.sub.2 CH.sub.2 CH.sub.3                                                             --CH.sub.3                                                                         1                                 2B   (2R,4S) & (2S,4R)                                                                              4-fluorophenyl                                                                           --CH.sub.2 CH.sub.2 CH.sub.3                                                             --CH.sub.3                                                                         1                                 3    --              4-chlorophenyl                                                                           --H       --CH.sub.3                                                                         1                                 4A   (2R,4R) & (2S,4S)                                                                              4-chlorophenyl                                                                           --CH.sub.3                                                                               --CH.sub.3                                                                         1                                 4B   (2R,4S) & (2S,4R)                                                                              4-chlorophenyl                                                                           --CH.sub.3                                                                               --CH.sub.3                                                                         1                                 5A   (2R,4R) & (2S,4S)                                                                              4-chlorophenyl                                                                           --CH.sub.2 CH.sub.3                                                                      --CH.sub.3                                                                         1                                 5B   (2R,4S) & (2S,4R)                                                                              4-chlorophenyl                                                                           --CH.sub.2 CH.sub.3                                                                      --CH.sub.3                                                                         1                                 6A   (2R,4R) & (2S,4S)                                                                              4-chlorophenyl                                                                           --CH.sub.2 CH.sub.2 CH.sub.3                                                             --CH.sub.3                                                                         1                                 6B   (2R,4S) & (2S,4R)                                                                              4-chlorophenyl                                                                           --CH.sub.2 CH.sub.2 CH.sub.3                                                             --CH.sub.3                                                                         1                                 7A   (2R,4R) & (2S,4S)                                                                              4-chlorophenyl                                                                           --(CH.sub.2).sub.3 CH.sub.3                                                              --CH.sub.3                                                                         1                                 7B   (2R,4S) & (2S,4R)                                                                              4-chlorophenyl                                                                           --(CH.sub.2).sub.3 CH.sub.3                                                              --CH.sub.3                                                                         1                                 8    (2R,4R) (2S,4S) (2R,4S) & (2S,4R)                                                              4-chlorophenyl                                                                           --(CH.sub.2).sub.2 CH═CH.sub.2                                                       --CH.sub.3                                                                         1                                 9    --              4-chlorophenyl                                                                           --H       --CH.sub.3                                                                         2                                 10A  (2R,4R) & (2S,4S)                                                                              4-chlorophenyl                                                                           --CH.sub.3                                                                               --CH.sub.3                                                                         2                                 10B  (2R,4S) & (2S,4R)                                                                              4-chlorophenyl                                                                           --CH.sub.3                                                                               --CH.sub.3                                                                         2                                 11A  (2R,4R) & (2S,4S)                                                                              4-bromophenyl                                                                            --CH.sub.3                                                                               --CH.sub.3                                                                         1                                 11B  (2R,4S) & (2S,4R)                                                                              4-bromophenyl                                                                            --CH.sub.3                                                                               --CH.sub.3                                                                         1                                 12A  (2R,4R) & (2S,4S)                                                                              4-bromophenyl                                                                            --CH.sub.2 CH.sub.3                                                                      --CH.sub.3                                                                         1                                 12B  (2R,4S) & (2S,4R)                                                                              4-bromophenyl                                                                            --CH.sub.2 CH.sub.3                                                                      --CH.sub.3                                                                         1                                 13A  (2R,4R) & (2S,4S)                                                                              4-bromophenyl                                                                            --CH.sub.2 CH.sub.2 CH.sub.3                                                             --CH.sub.3                                                                         1                                 13B  (2R,4S) & (2S,4R)                                                                              4-bromophenyl                                                                            --CH.sub.2 CH.sub.2 CH.sub.3                                                             --CH.sub.3                                                                         1                                 14A  (2R,4R) & (2S,4S)                                                                              2,4-dichlorophenyl                                                                       --CH.sub.2 CH.sub.3                                                                      --CH.sub.3                                                                         1                                 14B  (2R,4S) & (2S,4R)                                                                              2,4-dichlorophenyl                                                                       --CH.sub.2 CH.sub.3                                                                      --CH.sub.3                                                                         1                                 __________________________________________________________________________

                                      TABLE 1A                                     __________________________________________________________________________                               Analysis                                             Example                                                                             Low resolution                                                                          High resolution                                                                            C      H      N                                      No.  mass spectroscopy                                                                       mass spectroscopy                                                                          Calc                                                                              Found                                                                              Calc                                                                              Found                                                                              Calc                                                                              Found                               __________________________________________________________________________                   Found: m.sup.+ --C.sub.5 H.sub.7 N.sub.2,                                      209.0977; C.sub.12 H.sub.14 O.sub.2 F                            2A            requires 209.0977.                                               2B            Found: M.sup.+ --C.sub.12 H.sub.14 O.sub.2 F,                                  95.0610; C.sub.5 H.sub.7 N.sub.2                                               requires 95.0609.                                                3    279                  60.4                                                                              59.7                                                                               5.4                                                                               5.6 10.1                                                                              9.7                                  4A                                                                                 293                  61.6                                                                              61.0                                                                               5.8                                                                               5.7 9.6                                                                               9.6                                 4B                                                                              5A                                                                                 307                  62.7                                                                              62.0                                                                               6.2                                                                               6.2 9.1                                                                               8.9                                 5B                                                                              6A                                                                                 321                  63.7                                                                              63.2                                                                               6.6                                                                               6.6 8.7                                                                               8.7                                 6B                                                                              7A                                                                                 335                  64.7                                                                              64.8                                                                               6.9                                                                               7.2 8.4                                                                               8.3                                 7B                                                                             8    333                  65.1                                                                              64.9                                                                               6.3                                                                               7.0 8.4                                                                               7.9                                 9    292                  61.6                                                                              61.3                                                                               5.8                                                                               4.9 9.5                                                                               9.8                                  10A                                                                                307      62.7        62.1                                                                              6.2 5.8                                                                               9.2 10.0                                   10B                                                                             11A                                                                                338      53.4        53.6                                                                              5.0 5.6                                                                               8.3 7.3                                    11B                                                                             12A                                                                                352      54.7        54.1                                                                              5.4 4.8                                                                               8.6 8.0                                    12B                                                                             13A                                                                                366      55.9        56.3                                                                              6.6 5.7                                                                               7.8 8.0                                    13B                                                                             14A                                                                                341      56.5        56.0                                                                              5.3 4.8                                                                               8.2 9.1                                    14B                                                                            __________________________________________________________________________

EXAMPLE 15

The fungicidal activity of compounds of the invention was investigated by means of the following tests.

(a) Direct protectant activity against vine downy mildew (Plasmopara viticola; Pvp)

The test is a direct protectant one using a foliar spray. The lower surfaces of leaves of whole vine plants (cv Cabernet Sauvignon) are sprayed with a solution of the test compound in 1:1 water/acetone containing 0.04% "TWEEN 20" (Trade Mark; a poloxyethylene sorbitan ester surfactant) at a dosage of 1 kilogram of active material per hectare using a moving track sprayer and, after a subsequent 24 hours under normal glasshouse conditions, the lower surfaces of the leaves are inoculated by spraying with an aqueous solution containing 10⁴ zoosporangia/ml. The inoculated plants are kept for 24 hours in a high humidity compartment, 5 days under normal glasshouse conditions and then returned for a further 24 hours to high humidity. Assessment is based on the percentage of leaf area covered by sporulation compared with that on control leaves.

(b) Direct protectant activity against vine grey mould (Botrytis cinerea; Bcp)

The test is a direct protectant one using a foliar spray. The lower surfaces of detached vine leaves (cv Cabernet Sauvignon) are sprayed with the test compound at a dosage of 1 kg/ha using a track sprayer as in (a). 24 hours after spraying the leaves are inoculated with droplets of aqueous suspension containing 10⁵ conidia/ml. After a further 5 days in high humidity the percentage of leaf area covered by disease is assessed.

(c) Activity against wheat leafspot (Leptosphaeria nodorum; Ln.)

The test is a direct therapeutic one, using a foliar spray. Leaves of wheat plants (cv Mardler), at the single leaf stage, are inoculated by spraying with an aqueous suspension containing 1×10⁶ spores/ml. The inoculated plants are kept for 24 hours in a high humidity compartment prior to treatment. The plants are sprayed with a solution of the test compound at a dosage of 1 kilogram of active material per hectare using a track sprayer as described under (a). After drying, the plants are kept for 6-8 days at 20-25° C. and moderate humidity, followed by assessment. Assessment is based on the density of lesions per leaf compared with that on leaves of control plants.

(d) Activity against barley powdery mildew (Erysiphe graminis f.sp. hordei; Eg)

The test is a direct therapeutic one, using a foliar spray. Leaves of barley seedlings, (cv. Golden Promise) are inoculated by dusting with mildew conidia one day prior to treatment with the test compound. The inoculated plants are kept overnight at glasshouse ambient temperature and humidity prior to treatment. The plants are sprayed with the test compound at a dosage of 1 kilogram of active material per hectare using a track sprayer as described under (a). After drying, plants are returned to a compartment at 20-25° C. and moderate humidity for up to 7 days, followed by assessment. Assessment is based on the percentage of leaf area covered by sporulation compared with that on leaves of control plants.

(e) Activity against wheat brown rust (Puccinia recondita; Pr)

The test is a direct protectant one using a foliar spray. Wheat seedlings (cv Brigand) are grown to the 1-11/2 leaf stage. The plants are then sprayed with the test compound at a dosage of 1 kg/ha using a track sprayer as described under (a). Test compounds are applied as solutions or suspensions in a mixture of acetone and water (50:50 v/v) containing 0.04% surfactant ("TWEEN 20"-Trade Mark).

18-24 hours after treatment, the seedlings are inoculated by spraying the plants from all sides with an aqueous spore suspension containing about 10⁵ spores/ml. For 18 hours after inoculation, the plants are kept in high humidity conditions at a temperature of 20-22° C. Thereafter, the plants are kept in ambient glasshouse conditions, that is, in moderate relative humidity and at a temperature of 20° C.

The disease is assessed 10 days after inoculation on the basis of the percentage of the plant covered by sporulating pustules compared with that on the control plants.

(f) Activity against rice leaf blast (Pyricularia oryzae Po)

The test is a direct therapeutic one using a foliar spray. The leaves of rice seedlings (about 30 seedlings per pot) are sprayed with an aqueous suspension containing 10⁵ spores/ml 20-24 hours prior to treatment with the test compound. The inoculated plants are kept overnight in high humidity and then allowed to dry before spraying with the test compound at a dosage of 1 kilogram of active material per hectare using a track sprayer as described under (a). After treatment the plants are kept in a rice compartment at 24-30° C. and high humidity. Assessments are made 4-5 days after treatment and are based on the density of necrotic lesions per leaf when compared with control plants.

(g) Activity against tomato early blight (Alternaria solani; As)

This test measures the contact prophylactic activity of test compounds applied as a foliar spray.

Tomato seedlings (cv Outdoor Girl) are grown to the stage at which the second true leaf is expanded. The plants are treated using a track sprayer as described under (a). Test compounds are applied as solutions or suspensions in a mixture of acetone and water (50:50 v/v) containing 0.04% surfactant ("TWEEN 20"--Trade Mark).

One day after treatment the seedlings are inoculated by spraying the leaf upper surfaces with a suspension of A. solani conidia containing 10⁴ spores/ml. For 3 days after inoculation plants are kept moist in a glasshouse compartment at or near 100% RH and 21° C. Thereafter plants are kept under humid, but not saturated, conditions. Disease is assessed 7 days after inoculation, based on the density and spread of lesions.

(h) Activity against wheat eyespot in-vitro (Pseudocercosporella herpotrichoides; PhI)

This test meausres the in vitro activity of compounds against the fungus causing wheat eyespot.

The test compound is dissolved or suspended in acetone and is added to molten half strength Potato Dextrose Agar to give a final concentration of 100 ppm compound and 3.5% acetone. After the agar has set, plates are inoculated with 6 mm diameter plugs of agar/mycelium taken from a 14 day old culture of P. herpotrichoides.

Plates are incubated at 20° C. for 12 days and radial growth from the inoculation plug is measured.

(i) Activity against Fusarium in-vitro (Fusarium species; FsI)

This test measures the in vitro activity of compounds against a species of Fusarium that causes stem and root rots.

The compound is dissolved or suspended in acetone and added to molten half strength Potato Dextrose Agar to give a final concentration of 100 ppm compound and 3.5% acetone. After the agar has set, plates are inoculated with 6 mm diameter plugs of agar and mycelium taken from a 7 day old culture of Fusarium sp.

Plates are incubated at 20° C. for 5 days and radial growth from the plug is measured.

The extent of disease control in all the above tests is expressed as a rating compared with either an untreated control or a diluent sprayed-control, according to the criteria:

0=less than 50% disease control

1=about 50-80% disease control

2=greater than 80% disease control

The results of these tests are set out in Table II below:

    ______________________________________                                         Compound                                                                       Example  Fungicidal Activity                                                   No       Pvp    Bcp      Ln  Eg  Pr  Po  As  PhI  FsI                          ______________________________________                                         1A       2      2            2   1           1    2                            1B       2      2            2   1   2   1   2    2                            2A                           2           1   2    1                            2B                           2           2   2    1                            3                            2               2    1                            4A                           2               2    1                            4B       1                   2               1                                 5A       2                   2           1   2    2                            5B                           2   2           2    1                            6A       2                   2           2   2    2                            6B       1                   2       1   1   2    2                            7A                           2       1       1    2                            7B       1                   2       1       2    2                            8               1            2               2    2                            9                            2           2   1                                 10A                          2                                                 10B                          2               2                                 11A                          2               2    2                            11B      1                   2               2    2                            12A                          2       1       2    1                            12B      2      1            2       1   2   2    2                            13A      1                   2               2    2                            13B      2      1            2       1   2   2    2                            14A      1               2   2               2    1                            14B      1      1        2   2               2    2                            ______________________________________                                     

We claim:
 1. A compound of the formula ##STR7## or an acid-addition salt or metal salt complex thereof, in which R represents an optionally substituted phenyl group; R¹ represents a hydrogen atom or an optionally substituted alkyl or alkenyl group; R² represents an optionally substituted alkyl group; and n is 1 or
 2. 2. A compound according to claim 1 in which R represents a phenyl group optionally substituted by one or more substituents selected from halogen atoms, nitro, cyano, hydroxyl, alkyl, haloalkyl, alkoxy, haloalkoxy, amino, alkylamino, dialkylamino, formyl, alkoxycarbonyl, carboxyl, alkanoyl, alkylthio, aklylsulphinyl, alkylsulphonyl, carbamoyl and alkylamido groups.
 3. A compound according to claim 1 in which R represents a phenyl group substituted by 1 to 3 halogen atoms.
 4. A compound according to claim 3 in which the halogen atoms are chlorine atoms.
 5. A compound according to claim 1 or claim 2 in which R¹ represents a hydrogen atom, a C₁₋₆ alkyl group or a C₂₋₆ alkenyl group, each group being optionally substituted by one or more substituents selected from halogen atoms, nitro, cyano, hydroxyl, C₁₋₄ haloalkyl, C₁₋₄ alkoxy, C₁₋₄ haloalkoxy, amino, C₁₋₄ alkylamino, di-C₁₋₄ alkylamino, formyl, C₁₋₄ alkoxycarbonyl and carboxyl groups.
 6. A compound according to claim 1 or claim 2 in which R² represents a C₁₋₆ alkyl group.
 7. A compound according to claim 1 in which R represents a fluorophenyl, chlorophenyl, bromophenyl or dichlorophenyl group; R¹ represents a hydrogen atom or a methyl, ethyl, propyl, butyl or butenyl group; R² represents a methyl group; and n is 1 or
 2. 8. A fungicidal composition which comprises a carrier and, as active ingredient, a fungicidally effective amount of a compound of formula I, or an acid-addition salt or metal salt complex thereof, as defined in claim
 1. 9. A composition according to claim 8 which comprises at least two carriers, at least one of which is a surface-active agent.
 10. A method of combating fungus at a locus which comprises treating the locus with a fungicidally effective amount of a compound of formula I, or an acid-addition salt or metal salt complex thereof, as defined in claim 1 or with a fungicidally effective amount of a composition as defined in claim 8 or claim
 9. 11. A method according to claim 10 in which the locus comprises plants subject to or subjected to fungal attack, seeds of such plants or the medium in which the plants are growing or are to be grown. 